3.0 Head stud verification
 

I want to know if there is any way to tell if any head studs have been replaced on an 83 3.0 sc by walking up to the engine in the car?

If you open the valve covers you can generally see the tips of the head studs. ARP (aftermarket) head studs have a visibly round and chrome point that looks quite a bit different from the dull OEM studs. You may have to rub the tops a bit with a rag to remove any torquing grease to see them.

Perhaps someone else can chime in on what other makers look like (e.g. supertech).

You could also remove the tin from the exhaust side (above exhaust manifolds), but I know of no other way to see them.

ARPs also use a 12-point nut.

If somebody replaced all the head studs with dilavar (yes, some have done this) then you should be able to tell this by putting a magnet on the end of the stud, inside the hex of the head nut. You need a small magnet that'll hit just the stud itself and won't contact head nut. To do this you need to take the valve covers off. But this test isn't going to help you know how new they are.

Seeing them isn't possible from the outside on a SC engine top or bottom. The studs are not exposed anywhere below the head nuts. Can't see them thru the fins in the heads and not thru fins in the cylinders either. On the older cylinders you could see the studs.

Maybe
 

The later dilivar studs have a black coating on them that the originals did not have. If you can get under the car with a flashlight, you might be able to tell. Depends on how dirty/oily the engine is. I am rebuilding the engine from my 1980 SC and found one replacement dilivar stud on the bottom right. Evidence that it had been opened up at least once!

No way no how can you see the studs by just "walking up to the engine in the car".